Enzyme recovery from biological wastewater treatment

Abstract

Enzymes are high value industrial bio-catalysts with extensive applications in a wide range of manufacturing and processing sectors. The catalytic efficiency of enzymes can be several orders higher compared to inorganic chemical catalysts under mild conditions. However, the nutrient medium necessary for biomass culture represents a significant cost to industrial enzyme production. Activated sludge (AS) is a waste product of biological wastewater treatment and consists of microbial biomass that degrades organic matter by producing substantial quantities of hydrolytic enzymes. Therefore, enzyme recovery from AS offers an alternative, potentially viable approach to industrial enzyme production. Enzyme extraction from disrupted AS flocs is technically feasible and has been demonstrated at experimental scale. However, no consistent, optimal approach is available for the enzyme extraction from AS and the production of bio-enzymes from this biomass source can be affected by a range of factors, such as the operational extraction parameters. Moreover, free enzymes in the crude extract exhibit poor storage and operational stability, and are readily inactivated and difficult to recycle and reuse, which limits their large-scale commercial applications. The aim of this study is to develop a robust technology for enzyme recovery from AS and to explore the potential applications of recovered enzymes. A protocol for harvesting crude enzyme extracts from AS, by using sonication treatment to disrupt AS flocs, was set up; the impact of the sonication operational parameters and sludge sampling location on the enzyme extraction efficiency was investigated. A carrier-free, immobilised enzyme product, cross-linked enzyme aggregates (CLEA), was produced from the crude AS enzyme extract for the first time; the CLEA technique essentially combines purification and stabilisation of crude AS enzyme in a single step, and avoids introducing a large amount of inert carrier into the enzyme product. The AS CLEA contained a variety of hydrolytic enzymes and demonstrated high potential to be used for bioconversion of complex organic substrates.Open Acces